Albert, Ole Thomas

Vollen, Tone

English

Brage IMR

+45º-45ºDorsal view(i.e. sideways)0100200300Angle (5 deg. midpoints)-20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 600100200-20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 600100200300Angle (5 deg. midpoints)-20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60Frequency0100200300Angle (5 deg. midpoints)-20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 600100200-20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60Frequency0100200-20-15-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60Angle (deg.)-60-300306015MAY 25MAY 04JUN 14JUN 24JUN 04JUL 14JUL 24JUL 03AUG 13AUG 23AUGDepth (m)6005004003002001000Can Pitch & Roll DST distinguish between pelagic and demersal behaviour of adult Greenland halibut?By Ole Thomas Albert and Tone VollenCorrespondance: oleta@imr.no0ºPitchPrevious studies have shown that adult Greenland halibut may commonly occur several hundred meters above the bottom. Survey indices based on bottom trawls may therefore be biased. Our long-term goal is to quantify this bias.Without a swimbladder, the species is virtually invisible to echo sounders. Here we investigate if swimming behaviour, as recorded by Pitch & Roll Data Storage Tags, may be used to estimate the time spent in the pelagic environment.Greenland halibut (Reinhardtius hippoglossoides)•Deep-water flatfish•Pigmentation on both sides•Left eye on top of the dorsal ridge•Equally muscular on both sides•Both scientists and fishermen have therefore speculated if the species may adopt a vertical swimming position (i.e. Roll=90°).Pitch Pitch PitchRoll Roll RollPitch spectrum with no central tendency The fish is seldom or never resting on the sea floor and it lacks the steep descents.The fish is probably either swimming upwards or gliding slowly downwards, in accordance with expected pelagic behaviour.Angular spectrumThe shape of the angular spectrum may indicate if the fish is closely associated with the bottom or is continuously swimming.When the fish is close to the bottom and frequently resting on it, we would expect a symmetrical spectrum with central tendency close to zero. Since the bottom acts as refuge, steep descents are also expected.When the fish is swimming pelagicallythe usual flatfish swimming behaviour predicts steep ascents and gentle gliding descents. Without a bottom to rest on, horizontal pitch should be rear. Without the bottom surface to generate thrust against, body flexing may be more fierce.On bottom ?Constant depth48% of the time of all recapturesAlong bottom ?Diurnal or other slow changes in depth32% of the time of all recapturesPelagic ?High frequency changes in depth20% of the time of all recapturesPitchRollDepthA typical example of  Pitch & Roll DST recordings from Greenland halibut released and recaptured at the continental edge north of Norway. The data shown are from a 78 cm female in 2006. Data were recorded each 15 minutes. Three typical sequencesEach lasting one weekPitch spectrum with central tendency around zeroThe fish is often resting on the sea floor and shows both steep descents and ascents.The depth varies typically with a one-day period. The fish seems to be swimming up and down the slope, along the bottom.Pitch and roll spectrum with strong central tendency around zeroThe fish is often resting on the sea floor and shows some steep descents.Diurnal activity rhythms may be seen in pitch and roll, even though they may not appear in the depth and temperature recordings.They swim horizontally, like other flatfishesFrom 11 recovered Pitch and Roll DSTs, there were no indication of sustained swimming in a vertical position. Even during the first descents after release, the mean roll angle was less than 30º.CONCLUSIONS AND FURTHER WORK? Pitch & Roll DSTs may distinguish activity periods that are not apparent from the usual depth-temperature trajectories.? It seems plausible that Pitch & Roll DSTs may help distinguish between periods of pelagic swimming and more bottom oriented behaviour.? In addition to the field experiments, controlled tank experiments are needed to establish the relationships between pitch and roll, angle of movement, and whether or not the fish is swimming close to the bottom.0º-45ºRoll +45ºFront view

Can Pitch & Roll DST distinguish between pelagic and demersal behaviour of adult Greenland halibut

https://imr.brage.unit.no/imr-xmlui/bitstream/11250/116933/1/Q2206.pdf

Can Pitch & Roll DST distinguish between pelagic and demersal behaviour of adult Greenland halibut

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